1. Field of the Invention
The present invention relates to a window for automobiles or the like, including a window plate and a frame member provided integrally therewith, and also to a method of manufacturing such windows.
2. Description of the Related Art
Automobile windows wherein a window plate is integrally provided with a frame member is advantageous in that, since it is not necessary to prepare a window molding member as a separate component from the window plate, and number of components and assembly steps can be reduced to realize an improved manufacturing productivity in the assembly lines of automobile factories.
There is disclosed, e.g. in Japanese Patent applications, laid-open publication Nos. 58-113,480 and 63-112,143 and in Japanese Utility Model Application Laid-open Publication No. 62-118,724 a method of manufacturing such automobile windows, wherein the peripheral edge of a window plate is placed in the cavity of an injection mold, and the frame member is formed by a injection molding process, i.e. by injecting a synthetic resin material into the mold cavity. This known method suffers from a problem that the window plate tends to be subjected to damages due to a high injection pressure of the resin material.
Another method of manufacturing such windows is disclosed in Japanese Patent application Laid-open Publication Nos. 62-251,229; 62-257,831 and 63-112,143, wherein an elongate pre-shaped frame body of a constant cross-section is prepared separately from the window plate, from a thermoplastic synthetic resin material having a relatively high dielectric loss and containing a heat foamable agent therein, such that the foamable agent is maintained in a state in which it has not been substantially foamed. The pre-shaped frame body is secured to and along at least one peripheral edge of the window late, is placed in a mold cavity together with the relevant edges of the window plate, and is then applied with a high frequency voltage to cause the foamable agent to evaporate and expand within the mold cavity.
The above-mentioned method effectively prevent the window plate from damages since the window plate is not subjected to a high injection pressure as mentioned above. On the other hand, the known method is inevitably accompanied by formation of a number of bubbles in the interior of the frame body, though the size of the bubbles gradually decreases as their location comes closer to the outer surface of the frame member. The presence of a so-called skin layer, which includes a number of bubbles of a relatively small size near the outer surface of the frame member, is quite troublesome from a practical viewpoint for the following reasons. That is, it is often difficult to achieve a desired smooth and uniform appearance of the frame member, or to satisfactorily prevent formation of pinholes in the outer surface of the frame member without requiring strict control of the process conditions. Moreover, in the event that the outer surface of the frame member is to be subjected to painting and subsequent baking steps, the bubbles near the outer surface of the frame member tend to undergo an excessive expansion due to an elevated temperature during the baking, significantly deteriorating the desired ornamental appearance of the frame member.